1. Field of the Invention
The present invention relates to a routing control method and an apparatus thereof in a mixed environment of a hierarchical network and a non-hierarchical network, and especially relates to the routing control method and the apparatus thereof in the mixed environment of a hierarchy compliant IP (Internet Protocol) and a hierarchy-non-compliant IP.
2. Description of the Related Art
With the rapid proliferation of the Internet and Intranets into offices and campuses, the networks have evolved from conventional experiments to networks that play a central role in business. Further, the transmission speed of physical media, such as Ethernet, has risen from 10 Mbps, to 100 Mbps, and on to 1 Gbps. In order to service the high transmission speed, fast routing search inside a router is required. This requirement has led to the development of a hierarchical network that requires less time for routing search by simplifying network composition, and IPv6 (Internet Protocol version 6) as a hierarchy compliant IP technology to realize the hierarchical network.
However, the main thrust of networks at present is using IPv4 (Internet Protocol version 4) that is not compliant with hierarchy, resulting in a mixture of the non-hierarchical network and the hierarchical network in this transition period to the hierarchical network.
The IPv4, an IP widely used by the Internet at present, provides a 32-bit address, every 8 bits of which is delimited by a dot. The address, having a network block that identifies a network to which the node belongs, and a host block that identifies each node within the network, is assigned to each node. An IP address is suffixed by a slash and a number indicating how many bits the network block has.
For example, for an address 133.160.115.5/24, the first 24 bits (133,160,115) of the 133.160.115.5 represent the network block and 5 represents the host block. Moreover, if 0 is placed in the host block, the IP address indicates a network itself. That is, a network of 133.160.115 is indicated by 133.160.115.0/24.
The routers are installed on boundaries of networks to perform routing selection for a packet, and routing information required therefor is periodically exchanged among the routers. Exchange of the routing information is shown in FIG. 2. Routing information of the address 133.160.115.0/24 is exchanged from a router A to a router B, thereby, the router B recognizes that the address 133.160.115.0/24 exists beyond an address 150.123.212.0/24 (routing information to the router A).
Similarly, the router A recognizes that an address 133.160.116.0/24 exists beyond the address 150.123.212.0/24, using routing information from the router B. The same applies to exchanges between a router C and the routers A and B. Each router is provided with the routing information in a table format, and updates it at the next routing exchange.
FIG. 3 shows an example of a packet relay in a network that has exchanged the routing information as shown in FIG. 2.
1. An IP packet P1 transmitted to a host b from a host a is transmitted to the router A, which is a router of the address 133.160.115.0/24.
2. The router A searches for the network block of the address (133.160.116.0/24) through the entirety of its routing information table.
3. The router A determines that the router B is where the packet should be sent as a result of the search, and transmits the packet P1 to the router B.
4. The router B, upon receiving the packet P1, determines from the network block of the packet P1 that the packet is for its subordinate network, subsequently looks at the host block of the packet P1, and transmits the packet P1 to the host b.
Here, a point to be observed is that a routing search in each of the above clauses 2. and 4. was performed for the whole of the network block. This is because a decision as to which, router B or router C, the router A shall transmit to cannot be made by searching only part of the network block. In other words, the network is not structured in hierarchies based on IP addresses.
In a network that has evolved to be structured in hierarchies, it is not necessary to perform a routing search of an IP address including all the network blocks. Rather, it is performed in reference to a hierarchy. For example, FIG. 4 shows a hierarchical network based on a structure of IP addresses. When a host A on an address α.A.a.0/24 transmits a packet to a host B on an address β.B.a.0/24 in this network, routing selection can be performed by looking at only β in the address of the host B in a subordinate network of an address a α0.0.0/8. Further, a routing selection for the host B can start after the traffic enters under an address β0.0.0.0/8. Namely, it is not always necessary to perform the routing selection in reference to the entire network block.
As a means to realize the hierarchical network as above, a new IP protocol IPv6 is being studied and developed by a standardization organization, IETF (Internet Engineering Task Force) which decides on communication standards about IP. An example of an address format of IPv6 is shown in FIG. 5. As for IPv6, the address is 128 bit long, wherein TLAID (Top Level Aggregation Identifier) indicates the highest level in the hierarchy, and NLAID (Next Level Aggregation Identifier) and SLAID (Site Level Aggregation Identifier) are assigned to subordinate networks in this sequence by a network manager when a network is structured. An interface ID is assigned to each interface of each terminal, and generally a lower layer address, such as a MAC address, is included.
FIG. 6 shows an example of use of an IPv6 address format. As the drawing shows, TLA, NLA and SLA are layered in this order, and a MAC address (A) of a node Z is used as its interface ID. Further, FIG. 7 shows an example of the structure of a hierarchical network which uses IPv6. As shown in the drawing, TLA, NLA, and SLA structure the network with hierarchy, enabling the hierarchical routing search mentioned above.
Because of a high-speed routing search ability, the IPv6 will be introduced in the Internet from backbone to edge. However, in an introductory process, a mixed environment with IPv4 will be inevitable. For this reason, IETF has separately prescribed an address format that realizes mapping of IPv4 addresses onto IPv6 addresses as shown in FIG. 8. Hereinafter, this address format is called an IPv4 compatible IPv6 address format.
Although the IPv4 compatible IPv6 address format is a packet format to realize transmission and relay of a packet between IPv6 and IPv4 networks, the hierarchical structure as shown in FIG. 5 is not employed, but only a structure incorporating an IPv4 address in the address field of IPv6. For this reason, in a mixed environment with an IPv4 network, non-hierarchy-routing control is also required in the IPv6 network.
Expectation of the realization of fast routing control by a hierarchical network structure is growing, driven by the rapid expansion of the Internet/Intranets. As seen above, while a study and development of IPv6 have been undertaken, a problem has been that the high-speed routing control feature of IPv6 by the hierarchic structure could not be adapted in a mixed environment of the IPv4 network and the IPv6 network.